.\" $OpenBSD: BIO_s_fd.3,v 1.13 2023/11/16 20:19:23 schwarze Exp $
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.Dd $Mdocdate: November 16 2023 $
.Dt BIO_S_FD 3
.Os
.Sh NAME
.Nm BIO_s_fd ,
.Nm BIO_set_fd ,
.Nm BIO_get_fd ,
.Nm BIO_new_fd ,
.Nm BIO_fd_non_fatal_error ,
.Nm BIO_fd_should_retry
.Nd file descriptor BIO
.Sh SYNOPSIS
.In openssl/bio.h
.Ft const BIO_METHOD *
.Fo BIO_s_fd
.Fa "void"
.Fc
.Ft long
.Fo BIO_set_fd
.Fa "BIO *b"
.Fa "int fd"
.Fa "long close_flag"
.Fc
.Ft long
.Fo BIO_get_fd
.Fa "BIO *b"
.Fa "int *c"
.Fc
.Ft BIO *
.Fo BIO_new_fd
.Fa "int fd"
.Fa "int close_flag"
.Fc
.Ft int
.Fn BIO_fd_non_fatal_error "int errnum"
.Ft int
.Fn BIO_fd_should_retry "int retval"
.Sh DESCRIPTION
.Fn BIO_s_fd
returns the file descriptor BIO method.
This is a wrapper around the platform's file descriptor routines such as
.Xr read 2
and
.Xr write 2 .
.Pp
.Xr BIO_read 3
and
.Xr BIO_write 3
read or write the underlying descriptor.
.Xr BIO_puts 3
is supported but
.Xr BIO_gets 3
is not.
.Pp
If the close flag is set,
.Xr close 2
is called on the underlying file descriptor when the
.Vt BIO
is freed.
.Pp
.Xr BIO_reset 3
attempts to set the file pointer to the start of the file using
.Fn lseek fd 0 0 .
.Pp
.Xr BIO_seek 3
sets the file pointer to position
.Fa ofs
from start of file using
.Fn lseek fd ofs 0 .
.Pp
.Xr BIO_tell 3
returns the current file position by calling
.Fn lseek fd 0 1 .
.Pp
.Fn BIO_set_fd
sets the file descriptor of
.Vt BIO
.Fa b
to
.Fa fd
and the close flag to
.Fa close_flag .
.Pp
.Fn BIO_get_fd
places the file descriptor in
.Fa c
if it is not
.Dv NULL
and also returns the file descriptor.
.Pp
.Fn BIO_new_fd
returns a file descriptor BIO using
.Fa fd
and
.Fa close_flag .
.Pp
.Fn BIO_fd_non_fatal_error
determines whether the error status code
.Fa errnum
represents a recoverable error.
.Fn BIO_fd_should_retry
determines whether a recoverable error occurred by inspecting both
.Xr errno 2
and
.Fa retval ,
which is supposed to usually be
the return value of a previously called function like
.Xr BIO_read 3
or
.Xr BIO_write 3 .
These two functions are mostly used internally; in application code,
it is usually easier and more robust to use
.Xr BIO_should_retry 3 ,
which works for any BIO type.
.Pp
The behaviour of
.Xr BIO_read 3
and
.Xr BIO_write 3
depends on the behavior of the platform's
.Xr read 2
and
.Xr write 2
calls on the descriptor.
If the underlying file descriptor is in a non-blocking mode,
then the BIO will behave in the manner described in the
.Xr BIO_read 3
and
.Xr BIO_should_retry 3
manual pages.
.Pp
File descriptor BIOs should not be used for socket I/O.
Use socket BIOs instead.
.Pp
.Xr BIO_ctrl 3
.Fa cmd
arguments correspond to macros as follows:
.Bl -column BIO_CTRL_GET_CLOSE BIO_get_close(3) -offset 3n
.It Fa cmd No constant    Ta corresponding macro
.It Dv BIO_C_FILE_SEEK    Ta Xr BIO_seek 3
.It Dv BIO_C_FILE_TELL    Ta Xr BIO_tell 3
.It Dv BIO_C_GET_FD       Ta Fn BIO_get_fd
.It Dv BIO_C_SET_FD       Ta Fn BIO_set_fd
.It Dv BIO_CTRL_GET_CLOSE Ta Xr BIO_get_close 3
.It Dv BIO_CTRL_RESET     Ta Xr BIO_reset 3
.It Dv BIO_CTRL_SET_CLOSE Ta Xr BIO_set_close 3
.El
.Sh RETURN VALUES
.Fn BIO_s_fd
returns the file descriptor BIO method.
.Pp
When called on a file descriptor BIO object,
.Xr BIO_method_type 3
returns the constant
.Dv BIO_TYPE_FD
and
.Xr BIO_method_name 3
returns a pointer to the static string
.Qq file descriptor .
.Pp
.Fn BIO_set_fd
always returns 1.
.Pp
.Fn BIO_get_fd
returns the file descriptor or -1 if the
.Vt BIO
has not been initialized.
.Pp
.Fn BIO_new_fd
returns the newly allocated
.Vt BIO
or
.Dv NULL
if an error occurred.
.Pp
.Fn BIO_fd_non_fatal_error
returns 1 if
.Fa errnum
is
.Dv EAGAIN ,
.Dv EALREADY ,
.Dv EINPROGRESS ,
.Dv EINTR ,
or
.Dv ENOTCONN
and 0 otherwise, even if
.Fa errnum
is 0.
.Pp
.Fn BIO_fd_should_retry
returns 1 if
.Fn BIO_fd_non_fatal_error errno
is 1 and
.Fa retval
is either 0 or \-1, or 0 otherwise.
.Sh EXAMPLES
This is a file descriptor BIO version of "Hello World":
.Bd -literal -offset indent
BIO *out;
out = BIO_new_fd(fileno(stdout), BIO_NOCLOSE);
BIO_printf(out, "Hello World\en");
BIO_free(out);
.Ed
.Sh SEE ALSO
.Xr BIO_new 3 ,
.Xr BIO_read 3 ,
.Xr BIO_s_socket 3 ,
.Xr BIO_seek 3 ,
.Xr BIO_should_retry 3
.Sh HISTORY
.Fn BIO_s_fd ,
.Fn BIO_set_fd ,
and
.Fn BIO_get_fd
first appeared in SSLeay 0.6.0,
.Fn BIO_fd_should_retry
in SSLeay 0.6.5, and
.Fn BIO_new_fd
and
.Fn BIO_fd_non_fatal_error
in SSLeay 0.8.0.
All these functions have been available since
.Ox 2.4 .
